1. Field of the Invention
The present invention relates generally to a gastight valve strip that may be used on a reclosable container.
2. Description of the Background of the Invention
Food or other perishables are often stored in reclosable containers such as thermoplastic pouches. To keep food stored inside a pouch fresh for an extended period, a user may evacuate gas out of the pouch before completely sealing a closure mechanism of the pouch. Other reclosable pouches have been developed that have a valve that allows gas to be evacuated from the pouch after the closure mechanism has already been sealed.
Some pouch valves have a patch of thermoplastic material covering an aperture in a pouch wall and sealed over a limited area of the pouch wall around a periphery of the patch. The patch has an aperture therethrough that is offset from the aperture in the pouch wall. Pressure from outside of the pouch forces the patch against the pouch wall, keeping the valve closed. However, pressure from within the pouch forces the patch to separate from the pouch wall to allow air to flow through both apertures and out of the pouch. Another valve has a highly cohesive fluid in the space between the offset apertures to resist separation of the patch and the pouch wall. Still another valve has a porous layer of material secured over the aperture in the pouch wall, wherein the porous layer has a smaller area than the patch.
Other valves have a cover flap disposed over an aperture in a pouch wall, wherein the cover flap lacks an aperture. The valves have an unsealed edge that provides a path for escaping air. One such valve has a separator layer disposed between an adhesive layer disposed on an inner surface of the cover flap and an aperture in the pouch wall. The separator layer is smaller than the cover flap, but larger than the aperture, and is shaped so that the adhesive layer makes asymmetrical contact with the pouch wall around a periphery of the cover flap. Pressure from within the pouch forces a portion of the cover flap having a smaller adhesive contact area to separate from the pouch wall. The valve may also have an intermediate gas permeable layer between the separator layer and the aperture.
Another valve has a cover flap that is disposed across an entire width of a pouch wall. The flap overlays one or more apertures in the pouch wall to allow air to escape from within the pouch and to prevent air from entering the pouch.
Yet another valve for a pouch has a patch that is disposed across an entire width of a pouch wall and is sealed to the pouch wall around a periphery of the patch. A first plurality of apertures extending through the pouch wall is offset from a second plurality of apertures extending through the patch. An adhesive is disposed between the first and second pluralities of apertures. Pressure from within the pouch overcomes the adhesive and forces the patch to separate from the pouch wall to allow air to escape from within the pouch.
A still further valve has a patch that is sealed around a periphery of the valve over an inner or outer surface of a plastic tube. The patch may be oriented axially along a length of the tube, or circumferentially around the tube. The patch has a vent opening that is offset from a vent opening through the tube surface. A vent seal zone is defined between the patch and the tube surface. The tube is sealed on both ends such that pressure from within the tube forces the patch to separate from the tube surface to allow air to escape from within the tube.
Yet another valve has first and second zipper flanges sealed to an inside surface of a pouch wall. A line of apertures is disposed through the pouch wall, wherein the first zipper flange is attached to the pouch wall on a first side of the apertures and the second zipper flange is attached to the pouch wall on a second, opposite side of the apertures. An air path is formed between the first and second zipper flanges and the apertures. Pressure from within the pouch forces the second flange away from the first flange and pressure from outside the pouch forces the second flange into contact with the first flange. Alternatively, the second flange is eliminated, and the pouch wall on the second side of the line of apertures makes contact with the first flange. In another variation, one or more apertures disposed through the first flange are covered in flap fashion by the second flange.
Multiple layers of film material may be joined together, for example, by ultrasonic vibration, heat sealing, an adhesive, or by other means, as known to one skilled in the art, to form gastight sealed regions between the multiple layers. In one instance, multiple layers of film are bonded together by an intermittent ultrasonic bond. The intermittent bond has a number of bond points, spaced close together along a line to provide a leak-proof seal between the layers. Material displaced from each of the bond points may make contact with or may be close enough to material displaced from an adjacent bond point to block passage of fluid therebetween.
Sealed regions between multiple layers of film material may be formed by application of an adhesive between the layers. Adhesives generally provide an enduring gastight seal, but environmental conditions may cause the gastight seal to degrade. For example, an adhesive may suffer from loss of tact in cold conditions, or may become excessively fluid in hot or microwave conditions, resulting in flow of the adhesive into areas of the container where the adhesive may not be intended to go, such as into contact with food. A thermal seal may be more resistant than an adhesive seal to degradation caused by environmental conditions. A thermal seal between multiple layers of film material may be created by application of energy in the form of heat and/or ultrasonic vibration to a target sealing region. The applied energy may cause material within the target region to become molten, and to thereby bond the layers in a gastight seal. However, the molten material may flow away from the target region, and cause expansion and/or shrinkage of the film material surrounding the target region, which may form wrinkles in one or more layers of the film material outside of the target region.